WARNING: To avoid personal injury or death, disconnect your appliance from its power source before you start any troubleshooting or repair work. Use caution working inside any appliance.

Why won't my air conditioner turn on?

First, you want to make sure that you have power at the plug that you are using for your air conditioner. You can test it with a voltage meter or simply plug something else into the same outlet (if the receptacle is 220V, you will need to measure it with a voltage meter). If it works, you know you have power to the air conditioner. If it doesn’t work, you’ll need to check your fuse panel for any blown fuses or your circuit breaker box for any tripped circuit breakers.

If you have power, it could be one of several problems that are keeping it from running. Many times an air conditioner can't start the compressor if the amperage or voltage is too low. This can happen, especially if you run the unit from an extension cord or have something else that draws a lot of power on the same line. The compressor initially takes a lot of power to start.

If you hear any odd noises coming from the unit, it could be the compressor trying to start, but unable to do so. Another part that causes odd noises is the overload/relay. This causes a click-buzz-click sound near the compressor. This is the overload/relay working, and it protects the compressor from damage by cutting power to it if there’s a problem. If you hear this, the compressor has power, and it means something is wrong with the compressor. If the compressor is the cause of the problem, you'll need to contact a professional appliance repair person.

Also, any of the control components could be the cause of your problem. These include the control board, the selector switch, and thermostat. The control board controls the overall operation of an air conditioner, and if it is bad, it may prevent the unit from operating. The selector switch is used to adjust the settings that you want on your air conditioner. The thermostat controls the temperature. In addition, the wiring between any of these components could be to blame.

Sometimes the plug for the unit gets burned on the end that goes into the outlet, or the outlet itself gets scorched. This will reduce the contact points and may not allow any or enough power through to operate the unit. If this is the case, you need to replace the plug and outlet as it is also a fire hazard. You may want to call a professional electrician for this job.

If your air conditioner is running constantly, it may be that it’s too small for the room you’re trying to cool. Another reason may be that it is not cooling properly. Check the filter, coils for dirt buildup, and the air temperature leaving the unit. The cool air coming from the unit should be at least 15F cooler than the air going into it.

Make sure that you don't have windows open, allowing warm air back into the area that you're trying to cool. There may also be a control for a vent or louvre that allows outside air in. This vent being open will let warmer outside air in, and make the unit work harder to maintain a cool temperature. An open vent is also bad for allergy sufferers as it lets more pollens into the room. You also do not want to cover the front of the unit with any drapes or curtains as this will inhibit the airflow from the unit into the room.

Make sure there isn't any outside air leaking into the room by using sash sealer strips between the window and the unit. These strips work by filling in any gaps between the unit and the window frame and prevent cold air from leaking out of the room, and prevent warm air from entering the room.

You will have to measure the size of the room first. Then multiply the length by the width and that total is your square footage. You can use a chart or calculation provided by a manufacturer (usually available on their website) to determine how many BTUs you need your air conditioner to handle. You will also want to take into account how shady or sunny the room will be. Add ten percent more for a sunny room, and take ten percent away for shaded rooms.

Other factors that can influence the size of air conditioner that you need include: the number of windows letting light in, the insulation of the room, roof, and ceiling, how many people, and how many appliances or electronic devices are usually in the room.

Keep the unit clean of any buildups. The constant warming and cooling on these machines can build up moisture quickly. If it doesn't evaporate properly, the stagnant water can lead to fungi, molds, and mildews, as well as diseases like Legionnaire's disease growing in your unit. Don't forget to change the filter periodically.

Check the thermostat settings. Listen for compressor noise. Your fan can still work even if the compressor won’t start. Make sure the coils are clean and dust-free. If everything seems ok, perhaps the refrigerant level is low. As it is a sealed system, you can void the warranty by attempting repairs on it. You ought to call a professional appliance repair person.

Why isn't the whole room cool, even though the air conditioner is blowing cool air?

Check the condenser coils and air filter to see if they’re dirty. A buildup of dirt or lint will cause the air conditioner to not cool properly.

It is possible that the unit is not of a large enough capacity to cool down the size room that it is in. Did you just turn the A/C unit on it the room? If the room was very warm before turning the unit on, there is latent heat in the walls, floor, furniture, and ceiling. It may take some time to cool everything down.

Check to see if the air damper is open or closed. An open air damper lets outside air in.Make sure that the directional outlet from the unit is pointing up. Warm air rises, and cold air sinks.

Check the cool air temperature. Cool air should be 15 degrees cooler than the incoming air temperature. If not, your unit is not working properly.

Sometimes you can develop a leak in the refrigerant system. If you think this is the problem, call a professional appliance repair person.

Condensation of water on the evaporator coils in the front of an air conditioner is normal. This water collects in a pan where it is evaporated. On a really humid day, you may notice some is dripping off the unit. A properly installed unit will be tipped slightly back to allow any excess water to drip out the back.

Sometimes a fan can losen or it is necessary to oil for lubrication the bearings. Many, but not all fans, have an oil plug to top off the oil periodically. You can remove the plug and put a few drops of SAE 20 weight oil, or equivalent lubricating oil in the plug hole. You can check your owner's manual for specifics for your model.